1. Field of the Invention
The invention relates to methods and compositions for reducing serum levels of triacylglycerides in human subjects. In particular, the invention relates to the oral administration of an effective amount of a fungal lipase formulation, to a human subject having high or borderline-high serum levels of triacylglycerides, for a time period sufficient to reduce serum triacylglyceride levels.
2. Description of Related Art
Triacylglyceride Levels
A recent study by Ford et al. (Arch Intern Med, 169(6):572-578, 2009), at the Centers for Disease Control (CDC), involving 5,610 participants, showed that 33.1 percent of the participants had serum triacylglyceride levels defined as borderline high (>150 milligrams per deciliter). Nearly 18 percent had serum triacylglyceride levels defined as high (>200 milligrams per deciliter). High triacylglyceride levels may lead to atherosclerosis, which can increase the risk of heart attack and stroke. Persons with high triacylglyceride levels often have additional conditions that can increase their chances of developing heart disease, such as obesity and diabetes.
Hypertriglyceridemia is a human condition characterized by the presence of high serum levels of triacylglycerides. It has been associated with obesity, but can also be induced by other factors, independent of overall body fat (CT Johansen and RA Hegele, Curr. Opin. Lipidol., 22(4):247-253, 2011). The presence of single nucleotide polymorphisms in cellular genes such APOA5, APOB, GCKR, and LPL can induce severe hypertriglyceridemia in human beings. It is thought that more than 20% of the susceptibility to hypertriglyceridemia is caused by genetic mutations. Endothelial cell dysfunction and adipose cell dysfunction can lead to hypertriglyceridemia (HW Breuer Curr. Med. Res. Opin. 17(1):60-73, 2001; AP van de Woestijne et. al. Obes. Rev. 10.1111 (epub ahead of print) Jul. 12, 2011. Hypertriglyceridemia can be induced by specific drugs. For example, interferon alfa-2b and asparaginase have been shown to induce hypertriglyceridemia by two unique biochemical mechanisms (YK Keung et. al. South. Med. J. 92(9):912-914, 1999). Taken together, these studies indicate that high serum levels of triacylglycerides can be induced in human beings by multiple factors independent of obesity.
High serum levels of triacylglycerides (commonly called triglycerides; also referred to herein as “TAG”) have been identified as one of several lipid abnormalities commonly associated with patients that have type 2 diabetes (Bitzur et al., Diabetes Care 32 (suppl 2): S373-S377, 2009). It is currently unknown what mechanism(s) causes elevated serum TAG levels in these patients. The effect could be multi-factorial in nature, with contributions by diminished suppressive effects of insulin action, impaired clearance of lipid particles containing TAG, and the conscious dietary decisions by patients with type 2 diabetes to reduce carbohydrate caloric intake, replacing it with more meat and fats in their diets. Several prospective studies have identified hypertriglyceridemia as an independent predictor of type 2 diabetes. Recently, profiling of TAG molecules has been employed to help predict those that will acquire type 2 diabetes in the future (Rhee et al. J. Clin. Invest. 121(4):1402-1411, 2011). In view of these studies, clinicians monitor the level of triglycerides in a patient's serum, and researchers are looking for methods of lowering serum triglyceride levels.
Lipases
Lipases are enzymes that the body uses to break down fats to aid in the digestion of food. The specificity of lipases is derived from the molecular properties of the lipase, the structure of a potential substrate, and factors that affect the binding of the lipase to a substrate (Jensen R G et al. Lipids, 18(3):239-252, 1983). One of the most important lipases in the human body is pancreatic lipase. Pancreatic lipase breaks down triacylglycerides from ingested fats into smaller components that can be readily absorbed by intestinal cells (i.e., enterocytes), such as free fatty acids (FA) and 2-monoacylglyceride (2-MAG) (Pham, C. T. and Tso, P., Frontiers in Bioscience 6:d299-319, 2001; Levy et al. FASEB J. 9:626-635, 1995). The enterocyte synthesizes the FA and 2-MAG components into triacylglycerides (TAG) primarily via the Monoacylglyceride Pathway. The newly synthesized TAG are packaged into chylomicrons and then exocytosed into intracellular spaces and nearly lymphatic vessels. Chylomicrons containing TAG are ultimately distributed throughout the body for energy production and synthetic processes.
Historically, attempts to enhance/supplement lipid digestion have focused on oral administration of supplemental amounts of pancreatic lipase. However, naturally supplied pancreatic lipase is secreated directly into the intestine via the bile duct, while oral supplements must first transit the stomach. Pancreatic lipase is not stable in the acidic environment of the stomach whether it is empty (pH 1-2) or full (pH 3-4), and rapidly loses its enzymatic activity during exposure to these low pH conditions. Previous attempts to overcome the instability of pancreatic lipase activity at acid pH have shown unsatisfactory results. Approaches have included using enteric-coated tablets of pancreatic lipase (Graham D Y, New England Journal of Medicine 296:1314-1317, 1977), microsphere-encapsulated pancreatic lipase (see U.S. Pat. Nos. 5,260,074; 5,324,514; 5,352,460; 5,405,621), and cross-linked lipase crystals (see U.S. Patent Applications 2001/0046493 and 2003/0017144).
Accordingly, there remains a need for a lipase formulation that can be easily ingested and exert effective lipase activity, first in the acid pH environment of the full stomach and then in the neutral pH environment of the intestine.